1. Field of the Invention
This invention relates to external combustion engines, and more particularly, to multi-cylinder external combustion Stirling cycle engines.
2. Description of the Prior Art
One basic physical requirement of all engines operating in accordance with the Stirling cycle is that there must be approximately a 90.degree. phase shift between cooperating displacer pistons and power pistons. One prior art method of providing the requisite 90.degree. phase shift was to utilize a series of separate in-line displacer cylinders and power cylinders in combination with a crankshaft and a plurality of connecting rods for coupling together the various displacer pistons and power pistons to an output shaft while simultaneously providing the proper phase shift. One disadvantage of this method of providing the desired phase shift is that the in-line cylinder alignment necessarily requires a large, long fire box to provide heat to the upper portion of each of the displacer cylinders. The in-line cylinder configuration causes the engine to be large and quite difficult to incorporate in mobile installations.
A more modern versions of the Stirling engine incorporates a displacer piston and a power piston within a single cylinder by utilizing a pair of coaxial rods, one of which is coupled to the displacer piston and the other of which is coupled to the power piston. Since a 90.degree. phase shift must still be maintained between each displacer piston and its cooperating power piston, an extremely elaborate and complex rhombic drive assembly must be positioned directly beneath each cylinder. While eliminating the requirement for separate displacer cylinders and power cylinders, the rhombic drive greatly increases the amount of space required to house the lower portion of the engine. Furthermore, the rhombic drive includes a large number of different types of parts, all of which contribute to a reduction in overall reliability of the engine.
An additional difficulty encountered by prior art Stirling engines arose as a result of the typically limited number of cylinders incorporated into any given engine. A limited number of cylinders causes the power derived from the engine to occur in pulses, often necessitating the addition of a massive flywheel to the output shaft of the engine to smooth the periodic acceleration and deceleration of the output shaft.
The How And Why Of Mechanical Movements by Harry Walton, pages 160-166, explains the structure and operation of several prior art Stirling engine designs. The following U.S. Patents disclose prior art engine and transmission designs related to the present invention: U.S. Pat. Nos. 3,830,208 (Turner); 3,196,698 (Liddington); 2,653,484 (Zecher); 1,971,645 (Ehmig); 1,315,680 (Nordberg); and 1,943,664 (Fear).